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Snail Mortality

Keywords: binomial regression, factorial experiment.


Bill Venables writes:

Groups of 20 snails were held for periods of 1, 2, 3 or 4 weeks in carefully controlled conditions of temperature and relative humidity. There were two species of snail, A and B, and the experiment was designed as a 4 by 3 by 4 by 2 completely randomized design. At the end of the exposure time the snails were tested to see if they had survived; the process itself is fatal for the animals. The object of the exercise was to model the probability of survival in terms of the stimulus variables, and in particular to test for differences between species. The data are unusual in that in most cases fatalities during the experiment were fairly small.
Species Snail species A or B
Exposure Exposure in weeks (4 levels)
Humidity Relative humidity (4 levels)
Temp Temperature in degrees Celsius (3 levels)
Deaths Number of deaths
N  Number of snails exposed


Data file (tab-delimited text)


Venables, W., and Ripley, B. (1998). Modern Applied Statistics with S-Plus, Second Edition. Springer-Verlag.

The data is originally from the Department of Zoology, The University of Adelaide.



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